This application claims the benefit of Korean Patent Application No. 2000-38076, filed on Jul. 4, 2000 in Korea, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display (LCD) device having a color filter substrate and manufacturing method thereof.
2. Discussion of the Related Art
Generally, typical thin film transistor liquid crystal display (TFT-LCD) devices include an upper substrate and a lower substrate with liquid crystal molecules interposed therebetween. The upper substrate and the lower substrate are generally referred to as a color filter substrate and an array substrate, respectively. The upper substrate and the lower substrate respectively include electrodes disposed on opposing surfaces of the upper substrate and the lower substrate. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images depending on light transmittance.
In accordance with the application of an internal or external light source, LCD devices are commonly classified into two categories: a transmission type and a reflection type. The transmission type LCD has a liquid crystal display panel that does not emit light, and therefore, a backlight is provided to function as a light-illuminating source. The backlight is disposed at a first or rear side of the panel, and light emitted from the backlight passes through the liquid crystal panel to be controlled by the liquid crystal panel, thereby displaying an image. That is, the liquid crystal panel display forms an image according to an arrangement of the liquid crystal molecules which transmit or interupt light emitted from the backlight. However, the backlight of the transmission type LCD consumes 50% or more of the total power consumed by the LCD device. Accordingly, the use of the backlight increases power consumption of the LCD device.
To reduce power consumption, reflection type LCD devices have been developed for portable information apparatuses that are often used outdoors or carried along with users. Such reflection type LCD devices are provided with a reflector formed on one of a pair of substrates, and ambient light is reflected from the surface of the reflector. However, visibility of the display of reflection type LCD devices is extremely poor when the surrounding environment is dark and no ambient light is available.
In order to overcome the above problems, a transflective liquid crystal display device has been proposed that utilizes both a transmissive mode display and a reflective mode display in a single liquid crystal display device. The transflective liquid crystal display (LCD) device alternatively acts as a transmissive LCD device and a reflective LCD device by making use of both internal and external light sources, thereby providing operation with low power consumption in good ambient light conditions.
FIG. 1 is a schematic cross-sectional view showing a layer structure of a typical transflective LCD device. As shown, the transflective LCD device includes an upper substrate 30 and a lower substrates 10 and a horizontally oriented liquid crystal layer 60 interposed therebetween. The lower substrate 10 has a thin film transistor (TFT) (not shown) and a pixel electrode 20 disposed on the surface facing the upper substrate 30. The pixel electrode 20 includes reflective electrode portion 22 and a transparent electrode portion 21 disposed in an opening therebetween. The transparent electrode 21 is formed of ITO (indium-tin-oxide) or IZO (indium-zinc-oxide), and the reflective electrode 22 is made of aluminum (Al) having low electrical resistance and superior light reflectivity.
In FIG. 1, the upper substrate 30 includes a color filter 40 formed on the surface facing the lower substrate 10 corresponding to the pixel electrode 20, and a common electrode 50 formed on the color filter 40. Furthermore, a first retardation film 71 and a second retardation film 72 are formed on outer surfaces of the lower substrate 10 and the upper substrate 30, respectively. The first retardation film 71 and the second retardation film 72 are quarter wave plates (xe2x80x9cQWPxe2x80x9ds). The first QWP 71 and the second QWP 72 change a polarization state of light transmitted through the liquid crystal layer 60. Specifically, the first QWP 71 and the second QWP 72 convert linearly polarized light into right- or left-handed circularly polarized light, and conversely convert right- or left-handed circularly polarized light into linearly polarized light. A lower polarizer 81 and an upper polarizer 82 are formed on each outer surface of the first QWP 71 and the second QWP 72, respectively. Accordingly, a transmissive axis of the upper polarizer 82 makes an angle of 90 degrees with a transmissive axis of the lower polarizer 81. Furthermore, a backlight device 90 is disposed adjacent to the lower polarizer 81 and functions as a light source in the transmissive mode.
FIG. 2 shows operating principles of the transflective liquid crystal display device shown in FIG. 1. The transflective LCD device depicted in FIG. 2 includes a dispersion film 70 formed between the upper substrate 30 and the second QWP 72 to disperse the incident light (light xe2x80x9cLxe2x80x9d from the backlight device 90 and light xe2x80x9cMxe2x80x9d from the surroundings) and, thereby widens the viewing angle.
In FIG. 2, the light xe2x80x9cLxe2x80x9d generated from the backlight device 90 passes through the lower polarizer 81 and other elements on the lower substrate 10, through the liquid crystal layer 60, and through the upper polarizer 82. Concurrently, ambient light xe2x80x9cMxe2x80x9d passes through the upper polarizer 82 and other elements on the upper substrate 30, and then, through the liquid crystal layer 60. Then, the ambient light xe2x80x9cMxe2x80x9d is reflected onto a surface of the reflective electrode 22 and is redirected up toward the upper substrate 30, and passes back through the upper polarizer 82. At this time, the liquid crystal layer 60 has an optical retardation (defined by (dxc2x7xcex94n) hereinafter) xcex/4 (at xcex=550 nm).
In the above transflective liquid crystal display device, a normally white mode is adopted. Accordingly, the transflective device displays a white color when a signal is not applied. However, only about 50% of the light generated from the backlight device 90 can pass through the upper polarizer 82 in the transmissive mode of the transflective LCD device. Accordingly, a dark gray color is produced due to the transflective LCD device operating in the reflective mode, and also because a first cell gap xe2x80x9cd1xe2x80x9d (in FIG. 1) of the reflective portion is substantially equal to a second cell gap xe2x80x9cd2xe2x80x9d (in FIG. 1) of the transmitting portion.
In FIG. 2, a color purity of the light passing through the color filter 40 is dependent upon a thickness of the color filter 40. Accordingly, increasing a thickness of the color filter 40 improves the color purity of the light passing through the color filter 40. In the transflective liquid crystal display device shown in FIG. 2, the ambient light xe2x80x9cMxe2x80x9d passes through the color filter 40 twice due to the reflection on the reflective electrode 22, while the light xe2x80x9cLxe2x80x9d from the backlight device 90 passes through the color filter 40 just once. Therefore, there is a difference in color purity produced by the LCD device when operated in the transmissive mode versus operation in the reflective mode.
Furthermore, during operation of the transflective LCD device in the reflective mode, display images can only be seen in a projection direction and not in an incident direction because the ambient light xe2x80x9cMxe2x80x9d from the outside is reflected from the reflective electrode 22. To overcome this problem, the light dispersion film 70 is formed on the upper substrate 30. As a result, the manufacturing cost is raised and deterioration of display image brightness is increased in the transmissive mode.
Accordingly, the present invention is directed to a transflective liquid crystal display device and manufacturing method thereof that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a transflective liquid crystal display device and a manufacturing method thereof that increases brightness.
Another object of the present invention is to provide a transflective liquid crystal display device and a manufacturing method thereof that has uniform color purity in both the transmissive mode and reflective mode.
A further object of the present invention is to provide a method of manufacturing a color filter substrate that decreases manufacturing costs.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a transflective liquid crystal display (LCD) device includes a first substrate, a second substrate, a liquid crystal layer disposed between the first substrate and the second substrate, a passivation layer having a plurality of convex portions formed on a first surface portion of the second substrate, and a color filter layer formed on a second surface portion of the second substrate and on the passivation layer.
In another aspect of the present invention, a method of forming a color filter substrate for use in a transflective liquid crystal display (LCD) device includes the steps of forming a passivation layer on a first portion of a substrate, the passivation layer having different refraction characteristic portions, and forming a color filter layer on a second portion of the substrate and the passivation layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.